1. Field of the Invention
The present invention relates to a centrifugal tumbling granulating-coating apparatus, method of granulating and coating a powder or granular material by use of the apparatus, and more particularly to a technique of a centrifugal tumbling granulating-coating, in which spherical granulating of pharmaceuticals, foods and the like or coating on spherical granules is performed.
2. Related Art Statement
A centrifugal tumbling granulating-coating apparatus (hereinafter referred to a "CF apparatus") , in which a powder or granular material is centrifugally tumbled to produce spherical granules or is applied as a coating to spherical granules, is represented, for example, by "a centrifugal fluidized coating-granulating apparatus--CF-GRANULATOR" manufactured by Freund Industrial Co., Ltd., which is broadly sold on the market, and the construction thereof is shown in FIG. 5. In a CF apparatus 67 as shown in FIG. 5, a peripheral edge portion of a rotary disc 64 is positioned close to a side wall thereof through a small radius of curvature, whereby the powder or granular material tumbled with a centrifugal force increases friction loss in energy when it is tumbled in the vertical direction, and the tumbling action of the powder or granular material at a fixed wall is decreased, so that the upper limit of a charge amount is suppressed.
Now, from the beginning, the CF apparatus was developed to be mainly used for coating tablets and the like. However, recently, the CF apparatus is mainly used for spherically granulating or making coating layers of medicine and the like on the surfaces of spherical granules.
In these uses, it is required that spherical granules of good sphericalness are manufactured with high yield so as to be included within a predetermined range of grain size, and uniform coating layers are provided on the spherical granules. Then, in order to meet the above-described requirements, various proposals have heretofore been made for the construction and shape of the CF apparatus.
Namely, as an effective CF apparatus for coating the tablets and the like, in "a method and a apparatus for coating" as shown in Japanese Patent Publication No. 22544/1971 for example, there is described a rotary disc 24 rotatable horizontally is provided in the central portion, a curved speed reducing portion 25 provided around the rotary disc 24 and a coating pan 27 formed of a cylindrical portion 26 connected to the curved speed reducing portion 25 as shown in FIG. 6. Furthermore, in "a method and a apparatus for coating" as shown in Japanese Patent Publication No. 10878/1971, there is described a coating pan 37 including a rotary disc 34 rotatable horizontally and a curved fixed wall 35 surrounding the rotary disc 34 as shown in FIG. 7.
Further, as a CF apparatus effective for spherical granulation and the like, in "a apparatus for automatically coating particles" as shown in Japanese Patent Publication Publication No. 992/1979, there is described a apparatus for automatically coating powder 47, in which moisture in the coating apparatus is measured by a moisture detector to control feed rates of binding solution and drying hot air as shown in FIG. 8. Furthermore, in a thesis for a degree "compression molding and granulation of drugs" submitted by Mr. Yoshiro Funakoshi in Tohoku University, there is described a centrifugal tumbling type coating apparatus 57, in which a fixed wall 55 is curved inwardly, as shown in FIG. 9.
A throughput capacity for the powder or granular material, which is considered as a standard in CF apparatuses sold on the market at present is 30-50 kg on the product finishing base in a machine type, in which the diameter of the rotary disc is 1000 mm for example. In a case where an amount more than this is charged, the powder or granular material cannot be centrifugally tumbled satisfactorily, so that particles satisfactory in sphericalness cannot be produced. Then, the limit of the throughput capacity in these CF apparatuses has been accepted as one unavoidable, which is characteristic of CF apparatuses.
On the other hand, in recent years, the batch capacity has been increased due to the large-sized apparatuses for manufacturing pharmaceuticals and the like, and necessity for increasing the batch capacity of the CF apparatuses has been voiced by the market. Here, unless the specification of the CF apparatuses sold on the market is not freed from restraint, in order to meet this requirement, a further large-sized CF apparatus should be provided.
However, in the CF apparatus, in order to prevent the powder or granular material on the rotary disc from falling, it is required that a slit for ventilation provided between the side wall and the rotary disc is kept narrow and uniform width, so that it is very difficult to make the apparatus large-sized from the viewpoint of precision in working. Then, at present, the above-described requirement is met by providing a multiplicity of CF apparatuses while putting up with the increase in costs and areas of installation. And, the above-described limit of the throughput capacity cannot be dissolved by the above-described various proposals.
We analysed the conventional CF apparatuses from the viewpoint that whether the above-described limit of the throughput capacity can be cleared or not by effectively acting the centrifugal force for tumbling the powder or granular materials onto the individual particles. As a result, we knew that the configuration of the CF apparatus which has been known heretofore cannot satisfactorily utilize the action of the centrifugal force, and, in order to improve this, proposed a centrifugal tumbling granulating-coating apparatus 71 as disclosed in Japanese Patent Laid-Open Publication No. 232049/1995 (FIG. 10).
The centrifugal tumbling granulating-coating apparatus 71 as shown in the aforesaid Patent Laid-Open Publication No. 232049/1995 is constructed such that a rotary disc 75 has a peripheral edge portion 75b curved upwardly from a plain bottom surface portion 75a in a circularly arcuate shape in a vertical cross-section, so that the throughput capacity can be improved greatly. However, in this apparatus, since the radius of curvature R of the peripheral edge portion is as small as less than 0.25 of a diameter D of the rotary disc 75 as shown in FIG. 10, there has been found a problem that the treated powder or granular material is adhered to this portion and accumulated thereon.
This peripheral edge portion 75b is suitable for effectively acting the centrifugal force onto the powder or granular material when the powder or granular material to be treated is centrifugally tumbled, and it has been cleared by us that it is necessary to determine the shape of the rotary disc 75 to be free from adhesion and accumulation of the powder or granular material.